The invention relates to a multi-axis articulatable robot with a weld gun having a pair of opposing arms, movable relative to each other, and an inverted roller screw actuator for moving the arms as an additional axis controlled by the robotic controller.
A spot welding apparatus is used to produce a spot weld on a work piece, such as an automotive body panel. The spot welding apparatus traditionally includes C-shaped or X-shaped gun arms having a pair of welding tips on opposing arms spaced apart from each other. The welding tips define welding electrodes. The welding arms are movable toward each other and can be positioned on opposing sides of a workpiece during the spot welding operation. A welding apparatus can include one welding arm that is maintained in a fixed position while the second welding arm is movable. The welding apparatus can include welding arms movable with respect to one another either reciprocally, linearly or rotatably. Air cylinders and hydraulic cylinders have been used to produce movement in one or both of the welding arms.
In a spot welding operation, the pressure applied to the workpiece by the welding electrodes can be a factor in the success of the welding operation. The pressure acting on the workpiece is determined by the magnitude of thrust used to move the welding arms, specifically, the force applied by the air cylinder or hydraulic cylinder. Achieving an optimum welding operation can be difficult when a single workpiece requires multiple spot welding operations and each spot welding operation should be performed at a different pressure. It can be difficult to vary the pressure applied between various spot welds on a single workpiece by way of an air cylinder or an hydraulic cylinder. Generally, air cylinders and hydraulic cylinders are incapable of varying the pressure between welding electrodes quickly and precisely.
A robot system typically includes a controller to control the position, speed, acceleration, and force at any point along a path of travel of the robot and to control a servo motor corresponding to each axis of articulation of the robot. Typically, robots are provided with the capability of six axis articulation. However, the number of articulatable axes can be more or less depending on the particular application. In most configurations, the work tool supported by the robot for movement through the predetermined path includes a separate controller to control the particular tool. In the case of spot welding, the work tool controller can include an electrode pressing force controller and a welding electrical current controller. The separate controllers for control of the articulatable axes of the robot and movement of the welding tool requires additional time for opening and closing the tool while moving from one spot to another. It would be desirable to decrease the amount of time required for opening and closing the tool while moving from one weld spot to another in order to obtain productivity gains.
The present invention provides a robot having a plurality of axes for articulation to move the robot along a predetermined path. A single controller is provided for controlling the articulation of the robot about the plurality of axes. The same robot controller can control the movement of a weld gun as an additional axis of movement relative to the other articulatable axes of the robot to improve productivity.
The present invention provides a weld gun for performing a welding operation on a workpiece. The weld gun includes a pair of opposing arms movable relative to each other. The opposing arms apply pressure to a workpiece during a welding operation. The weld gun of the present invention also includes an inverted roller screw linear actuator. The inverted screw linear actuator can move the opposing arms relative to each other. The arms can be translatable or linearly reciprocal relative to each other, such as in a straight action C-shaped weld gun. Alternatively, the opposing arms can be rotatable relative to each other, such as in a pinch type x-shaped weld gun. The weld gun of the present invention can also include means for controlling the inverted screw linear actuator. The controlling means can include an electric control system engagable with a motor of the inverted screw linear actuator. The inverted screw linear actuator can include an elongate shaft having a first end for connecting to one of the opposing arms. The actuator can also include a rotatable threaded race for engaging the elongate shaft and a rotary motor for rotating the threaded race. The actuator can be mountable to one of the opposing arms. The weld gun of the present invention can also include an interchangeable electrode cap connectible to the end of each opposing arm and means for selectively retaining the electrode cap on each arm.
Other objects, advantages and applications of the present invention will become apparent to those skilled in the art when the following description of the best mode contemplated for practicing the invention is read in conjunction with the accompanying drawings.